A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
The lithographic apparatus may include a device for adjusting the uniformity of the radiation beam. Such a device may include a plurality of segments (also referred to as blades or vanes) that may be adjusted in order to block, deflect or attenuate part of the radiation beam. An example of such a device can be found in EP 1291721. In order to make the adjustments, the device can be equipped with a plurality of actuators for adjusting the blades or vanes.
The use of a radiation beam of e.g. UV-light or EUV-light may pose strict requirements with respect to the purity of the environment of the beam. Devices that operate near the radiation beam may therefore be subject to stringent requirements to avoid contamination due to e.g. outgassing or particles. These requirements may pose restrictions to the construction of the devices and to the materials that are applied. As an example, the use of ball- or sleeve bearing may be restricted due to the risk of particle contamination. Materials such as epoxy resins or insulators that are applied in commercially available actuators may pose a risk of outgassing. Ball- or sleeve bearings may also give rise to friction forces causing an unwanted non-linear system behavior. Furthermore, such bearings may give rise to unwanted play and therefore introduce inaccuracies in the positioning of the segment.
In addition to that, the device may be subject to severe operating conditions due to e.g. the thermal load on the segments of the device. As a consequence, the operating temperature of the actuators may be high compared to the allowable temperature of commercially available actuators. Due to the available volume and the requirements with respect to the dimensions of the adjustable segments, the available volume for the actuators may also complicate the use of commercially available actuators.